E36 interior problems boil down to the inserts on the doors coming unlaminated (easily fixed) and the fabric on the headliner coming down.. also easily fixed... if you can do it yourself. Not hard.just takes time and patience.
Even the renowned problem with the windows breaking their tracks can be fixed with some regreasing.
The cooling system.. not so much. You are looking at complete replacement of waterpump, thermostat, engine mounts, and probably radiator before 100K
I say engine mounts because if they are worn out, they will allow the fan to hit the shroud and it will "explode" and probably take the waterpump, radiator, and possibly the hood with it
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